Since Liquid Crystal Display apparatuses can realize large-sized display screen, light weight, thin structure and/or low power consumption, etc. as compared to Cathode-Ray Tube (CRT), they are used in Television Image Receiver and/or display apparatus for various display purposes along with, e.g., self-light emitting type Plasma Display Panel (PDP), etc. In the liquid crystal display apparatus, liquid crystals are included between two transparent bases (substrates) of various sizes to apply voltage across the transparent bases to vary orientation of liquid crystal molecules to change light transmission factor to optically display a predetermined image, etc.
In the liquid crystal display apparatuses, since the liquid crystal itself is not light emitting body, there is provided a backlight unit functioning as a light source, e.g., at the rear face portion of the liquid crystal panel. The backlight unit comprises, e.g., primary light source, light guide plate, reflection film, lens sheet and/or diffusion plate, etc. and serves to deliver display light over the entire surface of the liquid crystal panel. In the backlight unit, Cold Cathode Fluorescent Lamp (CCLF) adapted so that mercury or xenon is included within fluorescent tube is conventionally used as primary light source. However, it is necessary to solve the problems that light emitting luminance that the cold cathode fluorescent lamp has is low, lifetime is short, and/or low luminance region exists at the cathode side so that uniformity ratio, etc. is bad, etc.
Meanwhile, in liquid crystal display apparatuses of the large size, there is generally provided an Area Litconfiguration Backlight unit in which plural elongated cold cathode fluorescent lamps are disposed at the rear face of the diffusion plate to deliver display light to the liquid crystal panel. Also in such area litconfiguration backlight unit, it is necessary to solve the problems resulting from the above-described cold cathode fluorescent lamp. Particularly, in the case where the area litconfiguration backlight unit is applied to such a large sized television image receiver having size above 40 inches, the problems of realization of high luminance and/or realization of high uniformity ratio become more conspicuous.
On the other hand, in the area litconfiguration backlight units, in place of the above-described cold cathode fluorescent lamp, attention is drawn to backlight of the Light Emitting Diode (hereinafter referred to as LED as occasion may demand) area light type in which a large number of red, green and blue LEDs of light three primary colors are two-dimensionally arranged at the rear face side of the diffusion film to obtain white light. Such LED backlight unit permits reduction of cost with realization of reduction of cost of LED, and permits display of high luminance on large-sized liquid crystal panel by low power consumption.
In various backlight units, there are arranged, between the light source unit and the transmission type liquid crystal panel, various optical members such as optical functional sheet block, diffusion light guide plate, light diffusion plate, and/or reflection sheet, etc which are adapted for performing functional conversion of display light which has been emitted from the light source, and serving to allow the display light to be uniform. The light diffusion plate used in the backlight unit is generally formed by transparent acrylic resin, etc. At the position opposite to the light source, there are formed light adjustment patterns having a function to allow a portion of incident display light to be transmitted therethrough, and to allow the other portion thereof to be reflected thereon. As a light diffusion plate, there is light diffusion plate described in the Japanese Patent Application Laid Open No. 1994-301034 publication. In the light diffusion plate described in this publication, band-shaped light adjustment pattern constituted by a large number of reflection dots is provided within the region opposite to the fluorescent tube. Reflection dots are formed so that according as distance from the axis of fluorescent tube increases, the area becomes small, whereby the light diffusion plate functions so that light transmission factor becomes higher according as distance from the fluorescent tube increases. Thus, homogenized illumination light is emitted on the whole.
Meanwhile, also in the LED backlight unit, it is conceivable that light diffusion plate is disposed between the transmission type liquid crystal panel and the light source unit in which light source blocks where a large number of LEDs are mounted are arranged as array to form a large number of light adjustment patterns at the light diffusion plate so as to respectively face the respective LEDs. At the respective light adjustment patterns, transmitting operation and reflecting operation of rays of display light which are emitted from LEDs facing thereto are controlled so that rays of display light are delivered from the entire surface of the light diffusion plate to the liquid crystal panel at a uniform light quantity. Thus, realization of high luminance and realization of high uniformity ratio are performed.
However, in the LED backlight unit, heat of large capacity produced from a large number of LEDs is exerted on the light diffusion plate formed by acrylic resin, etc. to produce large dimensional change at the light diffusion plate so that positional shift may take place at LEDs and the light adjustment pattern which are opposite to each other. Moreover, in the LED backlight unit, positional shift between LEDs and the light adjustment patterns which are opposite to each other may take place by unevenness of dimensional accuracy and/or assembling accuracy of the liquid crystal panel, the light source unit or the light diffusion plate, and print accuracy of the light adjustment pattern, etc.
In the LED backlight unit, it was difficult to extremely perform positioning of the LEDs and the light adjustment patterns with high accuracy because the above-described various factors are concerned. In the LED backlight unit, it is required to manufacture constitutent members with high accuracy and to perform precise assembling. As a result, it was difficult to reduce the cost. In the LED backlight unit, the positional shift between LED and light adjustment pattern becomes larger with realization of enlargement and/or realization of high luminance of the liquid crystal display apparatus. Thus, there become conspicuous the problems that color unevenness and/or ramp image may take place in the liquid crystal panel, etc.
Moreover, in the LED backlight unit, since the light source unit is adapted so that plural light source blocks where a large number of LEDs are mounted are arranged with a space provided therebetween to constitute area litconfiguration backlight unit, there takes place the phenomenon where rays of display light which have been radiated from respective LEDs toward the outer circumferential direction are concentrated from both sides between columns of the respective light source blocks so that there takes place the phenomenon where the portions where luminance is large take place. In the LED backlight unit, for the reason as stated above, high luminance region in the lateral stripe state takes place within opposite regions between respective columns of the respective light source blocks of the light diffusion plate. Thus, color unevenness of lateral stripe may disadvantageously take place at the liquid crystal panel.
In the LED backlight unit, it is conceivable to form light adjustment pattern by a large area at, e.g., light diffusion plate, and to form such plate by opalescent synthetic resin with respect to the above-described problems. However, since display light is shielded so that light transmission factor is reduced to much degree, luminance of the liquid crystal panel is lowered. In the LED backlight unit, in the case where, e.g., a larger number of LEDs are used so that compliance of realization of high luminance is performed, not only cost is increased and/or power consumption becomes larger, but also it becomes difficult to extremely comply with larger heat.